Cold tolerance of the pine armored scale Hemiberlesia pitysophila (Homoptera: Diaspididae) in different regions

In order to explore geographic adaptability to low temperature of Hemiberlesia pitysophila (pine armored scale, a dangerous insect pest), its supercooling point (SCP, Xinyi in Guandong Province, and Zhangzhou, Quanzhou and Changle in Fujian Province) and exposure mortality (EM, Xinyi, Quanzhou and Changle) to a designated low temperature were measured in the winter of 2007. Results indicate that female adult SCP for the four regions is significantly different (P<0.05). It is lowest for Changle with a mean value of ?15.71 ℃, while is highest for Xinyi with a mean value of ?13.68 ℃. SCP exhibits a declining tendency with rising latitude. Under 10 ℃ to ?20 ℃, the mortality of the insect pest is remarkably higher in Xinyi than in Changle and Quanzhou. When specifically exposed to ?10 ℃, its mortality in Xinyi is 85.97%, but only 37.58% and 56.65% in Quanzhou and Changle respectively. Furthermore, the relationship between sum of temperature and population mortality in Xinyi, Quanzhou and Chanle is in accordance with revised double variable Logistic model. The same is the case for the five insect developmental stages including instar nymph (1st stage), instar nymph before sex differentiation (2nd stage), instar female (2nd stage), male nymph after sex differentiation and female adult. Median lethal sum of injury temperature (SLIT50) of the population is also higher in Xinyi than in Quanzhou and Changle. The findings imply that H. pitysophila is strongly adaptable to low temperatures with an increasing cold tolerance at higher latitudes.